An upcoming episode of “Teen Wolf” Season 5B will feature the guest appearance of actors Gilles Marini and Lachlan Buchanan.

Marini and Buchanan will join Tyler Posey and other cast members in an upcoming “Teen Wolf” Season 5B episode, which will feature a flashback about the Beast’s 1700's background, according to TV Line. Marini, known for his role in the series “Switched at Birth” and a former “Dancing with the Stars” contender, will play the French soldier Sebastien. Meanwhile, “The Young and Restless” actor Buchanan will play a member of the Argent family named Henri.

The flashback episode will show Marini’s character returning home to the French countryside of Gevaudan and discovering that the Beast has been terrorising his sister and loved ones. Buchanan’s character is a recluse who lives in a forest grove and has been described as “wise but guarded.” Being an Argent, Buchanan’s Henri is said to know a lot about the supernatural world, according to TV Line.

“Teen Wolf” showrunner Jeff Davis told TV Line that Marini was “excited” to be part of the Beast flashback story, and he knows a lot about the fabled creature given his background. Marini is a French-American actor and grew up with tales about the Beast of Gevaudan. “He’s French, and for his family, the Beast of Gevaudan was their Boogeyman. They would all tell stories about the Beast, so it was a very familiar character to him,” Davis explained.

Apart from Marini and Buchanan, the Beast flashback episode of “Teen Wolf” will also feature an alum from the MTV series, namely Crystal Reed. The actress previously portrayed the role of Allison Argent, Posey’s Scott former love interest. In the flashback episode, Reed will guest star as one of Allison’s ancestors, Marie-Jeanne Valet.

Meanwhile, the Beast is considered the real enemy in “Teen Wolf” Season 5B. Showrunner Davis previously revealed that the creature was a chimera “formed by shadows.” He also shared that uncovering the mystery surrounding the Beast and the creature’s identity would be one of the major storylines of the season.

The Beast flashback will be featured in the Feb. 23 episode of “Teen Wolf.” Meanwhile, the next episode titled “Codominance” will air on Jan. 19 in the US on MTV.